Interplay between dispersive and non-dispersive modes in the polaron problem

We study the influence of the phonon spectrum on polaron formation and show that three self-trapping regimes con occur. If the lattice and the electro n-lattice Hamiltonians are dominated by the same type of phonons, the self- trapping transition is smooth. If there is an imbalance, the transition can either be abrupt ol completely eliminated. The binding energies are larger in the case of imbalance. The bandwidth varies linearly with hopping stren gth, even fur strongly localized states. (C) 2000 Elsevier Science B.V. All rights reserved.